The Skin as a critical window in unveiling the pathophysiologic principles of COVID-19

Magro, Cynthia; Nuovo, Gerard; Mulvey, Justin; Laurence, Jeffrey; Harp, Joanna; Neil Crowson, A.

The severe acute respiratory distress syndrome-associated coronavirus-2 (SARS-CoV-2), the etiologic agent of Coronavirus disease 2019 (COVID-19), is a single-stranded RNA virus whose sequence is known. COVID-19 is associated with a heterogeneous clinical phenotype ranging from asymptomatic to fatal disease. It appears that access to nasopharyngeal respiratory epithelia expressing angiotensin-converting enzyme (ACE) 2, the receptor for SARS CoV-2, is followed by viral replication in the pulmonary alveolar septal capillary bed. We have shown in prior studies that incomplete viral particles, termed pseudovirions, dock to deep subcutaneous and other vascular beds potentially contributing to the prothrombotic state and systemic complement activation that characterizes severe and critical COVID-19. A variety of skin rashes have been described in the setting of SARS-CoV-2 infection and more recently, following COVID-19 vaccination. The vaccines deliver a laboratory synthesized mRNA that encodes a protein that is identical to the spike glycoprotein of SARS-COV-2 allowing the production of immunogenic spike glycoprotein that will then elicit T cell and B cell adaptive immune responses. In this paper we review an array of cutaneous manifestations of COVID-19 that provide an opportunity to study critical pathophysiologic mechanisms that underlie all clinical facets of COVID-19 ranging from asymptomatic/mild to severe and critical COVID-19. We classify cutaneous COVID-19 according to underlying pathophysiologic principles. In this regard we propose two main pathways: 1) complement mediated thrombotic vascular injury syndromes deploying the alternative and mannan binding lectin pathways in the setting of severe and critical COVID-19 and 2) the robust T cell and type I interferon driven inflammatory and humoral driven immune complex mediated vasculitic cutaneous reactions seen with mild and moderate COVID-19. Novel data on cutaneous vaccine reactions are presented that manifest a clinical and morphologic parallel with similar eruptions seen in patients suffering from mild and moderate COVID-19 and in most cases represent systemic eczematoid hypersensitivity reactions to a putative vaccine based antigen. Finally, we show for the first time the localization of human synthesized spike glycoprotein following the COVID-19 vaccine to the cutaneous and subcutaneous vasculature confirming the ability of SARS CoV-2 spike glycoprotein to bind endothelium in the absence of intact virus.